In September 2012, Amnesty International, USA[9] (AIUSA) requested that the Geospatial Technologies and Human Rights Project of the American Association for the Advancement of Science (AAAS) investigate human rights-related reports stemming from the escalating conflict in Aleppo, Syria (Figure 1[10]). Two images from August 2012 were obtained and analyzed. This analysis documented over one hundred instances of damage to buildings and infrastructure, numerous shell craters, multiple improvised roadblocks, and the presence of heavy armored vehicles in civilian neighborhoods, and resulted in the AAAS report "Satellite Imagery Analysis for Urban Conflict Documentation: Aleppo, Syria".1[11]

Figure 1: Overview

Since August 2012, what has been called the "Battle for Aleppo"2[12] has continued with further reports of heavy fighting,3[13] civilian casualties,4[14] and the destruction of segments of the Anceint City of Aleppo, a UNESCO World Heritage Site.5 As the conflict in the region has continued, AIUSA again requested to partner with the Geospatial Technologies and Human Rights Project to investigate human rights-related reports.

Using information provided by AIUSA and media reports, seven additional images of Aleppo and its environs were acquired to supplement the two images obtained previously (Table 1[16]). These images provide a snapshot of Aleppo at regular intervals between August 2012 and June 2013. Image acquisition was also influenced by media reports of major incidents, such as damage to the Umayyad Mosque within the Old City, with the goal of validating these reports. All images cover the same one hundred and eighty-two square kilometers analyzed in the prior AAAS report except for the image from February 24, 2013, which covers the northernmost one hundred and twenty-six square kilometers of the study area.

* Image was used in previous Aleppo report
** Image does not cover full 182 km2 study area

II. Image Analysis

Analysis of the city focused on four categories of observations. The first of these surveyed the deployment of military equipment, and included observations of machinery, including artillery, tanks and other armored vehicles, helicopters, and fixed-wing aircraft. The second category consisted of barriers in the street, and was created because the previous analysis of Aleppo had revealed the presence of numerous improvised roadblocks. The third counted signs of damage and destruction, including observable harm to buildings, debris in the road indicating damage to facades, and shell craters. Finally, special attention was paid to damage to Aleppo's many cultural sites, especially within the Ancient City of Aleppo, a UNESCO World Heritage Site.

The size and population density of Aleppo presents several unique challenges to image analysis and interpretation. The city contains many neighborhoods comprised of high-rise buildings in close proximity to one another, which often cast deep shadows on the nearby streets. This situation was further exacerbated by the fact that the satellites' operators had sometimes rolled the spacecraft away from a directly downward orientation in order to enable their cameras to capture the city of Aleppo as they passed over (see Table 1[16] for specific off-nadir angles). While this image collection method resulted in timely imagery of the evolving conflict, it had the side-effect of introducing a horizontal component to the imagery, in which the vertical faces of structures appear to "lean over" adjacent open space (see Figure 17[17], for example). When combined with the effects of shadows, this rendered large portions of the city invisible from above; in these areas, relevant events may have taken place that could not be detected. In addition, the high density of very small buildings often made it difficult to see between them and identify damage in some parts of the city, particularly the Old City. Despite these challenges, it was possible to observe many signs of the conflict throughout the study area.

III. Results

I. Military Vehicles and Equipment

Throughout the course of the study, evidence of military activity was apparent at numerous locations around the city. At an athletic field of the Al-Assad military academy, for example, an unusual cluster of vehicles and an area of disturbed soil was first observed on 12 October (Figure 3A[18]). The origin of this disruption became apparent on 4 November, when a helicopter with a profile and rotor configuration matching that of an Mi-17 or Mi-24 multirole attack/transport helicopter appeared in the same location (Figure 3B[18]), suggesting that the field was being used as an improvised staging area. On 15 December, the helicopter was no longer present, but the vehicles (now presumed to be supporting the helicopter) remained visible on the sidelines.

A similar phenomenon was observed at the artillery academy located approximately three kilometers to the southeast, where a helicopter was observed at a truck depot on 15 December 2012 (Figure 4A[19]), along with recently-applied helipad markings (Figure 4B[19]).

In addition to these observations, a number of military helicopters (also probable Mi-17s or Mi-24s) were observed on the tarmac at Aleppo International Airport. The numbers and relative positions of these aircraft changed frequently, suggesting regular use. Similar behavior was observed for fixed-wing combat aircraft such as MiG-23s and L-39s, as well as an Il-76 strategic airlifter, all of which were intermittently present on the airport's flight line (Figure 5[20]). These observations are consistent with reports that government forces have been using both fixed and rotary wing aircraft to support combat operations in and around Aleppo. A summary of military aircraft observations by month is presented in Table 2[21].

Military land vehicles were also present, ranging from tanks and other armored vehicles to artillery and surface-to-air missile batteries. Their deployments were both observed directly, as when three tanks were spotted reinforcing an intersection at the southern approaches to the city (Figure 6[22]), and inferred via phenomena such the changing numbers and positions of vehicles at staging areas (Figure 7A-B[23]), and tracks left in soil following maneuvers (Figure 8[24]).

A key characteristic of the fighting in Aleppo has been the creation of roadblocks to control movement within the city. Many of these consist of vehicles placed to block streets and intersections (Figure 9A[25]). These appear to be mostly trucks or busses placed across strategic intersections. In some cases, however, it is possible that the barriers are actually disabled vehicles that have not been removed. Other roadblocks include multiple earthen barricades placed at major intersections (Figure 9B). In a few cases, deep trenches have been dug to completely block major highways (Figure 9C[25]). Only three instances of this type of barrier were counted, all north of the Youth Housing Project neighborhood.

The total number of barriers observed in the city has steadily increased over the course of the study period (Table 3[26]). This trend holds true even between 12 December 2012 and 24 February 2013, where the total number of barriers observed increased despite 150 existing roadblocks falling outside the image extent. These additional roadblocks are the result of both barriers being added to previously unblocked streets (Figure 10[27]), as well as the augmentation of existing roadblocks with additional obstructions (Figure 11[28]). It should be noted that some of these barriers are not permanent; a relatively small number have been removed over the course of the study period.

* Image was used in previous Aleppo report
** Image does not cover full 182 km2. 233 new roadblocks were observed within the image extent but 150 roadblocks from 15 December 2012 were outside the image extent

The proliferation of roadblocks has not been evenly distributed across the city; much of the increase is concentrated on the west side of the city, both inside and outside the highway that encircles Aleppo (Figure 12[29]). Roadblocks also tend to be concentrated on major roads. The number of roadblocks on the highway circling Aleppo, as well as the highway entering Aleppo from the east has steadily increased. Roadblocks have also proliferated at interchanges between these highways and smaller roads leading in and out of neighborhoods.

Fewer roadblocks were observed in the east of the city and in central neighborhoods. In central neighborhoods, particularly the old city, this may be a result of narrow streets and the aforementioned shadows limiting the number of barriers that can be observed. In eastern sections of the city, however, structures tend to be smaller and the streets are wider, so shadows are less of a factor. As a result, the lack of observed roadblocks likely reflects the situation on the ground.

Numerous residential and industrial areas of Aleppo have been progressively damaged or destroyed over the course of the conflict. The effects of this continuous degradation to the city's buildings and infrastructure were primarily visible in three ways: the formation of debris aprons, the direct observation of destruction, and the presence of craters resulting from bombs or artillery fire. The first of these, debris aprons (examples of which are shown in Figure 13[30]), form when the exterior walls of a structure are compromised, causing their remains to fall into the adjacent streets where they can be seen from above. Because this type of damage often leaves the major structural components of a building intact, it can be difficult to evaluate the extent to which structures associated with these features have been damaged. Furthermore, shadowing effects may obscure many debris aprons from view, particularly in narrow streets or alleyways, which Aleppo possesses in abundance. Despite this limitation, however, the 'top-down' perspective of satellite imagery often makes debris aprons the only available means of determining that an un-collapsed structure has been damaged at all.

In cases where destruction was directly visible, it was sometimes accompanied by signs of combat including roadblocks, scorch marks on pavement, and rubble filling the streets. In some neighborhoods, the destruction was so complete that it was difficult to discern the remains of individual structures from the surrounding debris, as in the case of Karm al-Jabal district, where large swaths of the district were reduced nearly to rubble (Figure 14[31]). Occasionally, signs of fire were also present, and in a few rare instances, potential agents of the destruction were observed in close proximity to the damaged areas (e.g., the tanks visible in Figure 6[22]). At other times, such as in imagery from 24 February, destruction appeared to occur in highly localized patches surrounded by undamaged areas, both of which lacked any indications of street fighting (Figure 15[32]). From the imagery alone, no firm conclusions can be made with regard to the origin of this phenomenon. However, its discrete nature and nearly circular shape are consistent with the effects of missile strikes, several which reportedly took place in the same districts where this unique pattern of damage was observed, just two days before the imagery was acquired.6[33], 7[34] Also observed, though rarely, was destruction in progress. In the Al-Myassar Jazmati district near Aleppo's airport, for example, a fire engulfing several buildings of an industrial plant was observed producing large billowing clouds of smoke on 24 February, which was still smoldering five days later, on 1 March (Figure 16[35]).

As with roadblocks, observations of damage and destruction increased throughout the study period. When plotted against time, the trend in these observations was remarkably linear (Figure 18[36]), suggesting a nearly constant rate of about three visible destructive incidents per day. Due to the limitations of the "top-down" perspective provided by the majority of the available imagery, this is likely an underestimate, however, as many structures in Aleppo are capable of sustaining damage without total structural failure (e.g., Figure 13[30], above). In instances where this type of damage occurs without the formation of a visible debris apron, it is unlikely to be detected (Figure 17[17]).

As illustrated in Figures 18[36] and 20[37], the number of observations of destruction increased steadily over time. In addition to its remarkably stable increase from image to image, however, one of the more striking features of the destruction was its spatial distribution. When the overall map of observed incidents is compared with the administrative divisions of the city at the neighborhood level, a clear pattern emerges, with certain districts being heavily affected by the conflict, while others remain largely - or in many cases totally - unaffected (Figure 19[38]). The contrast becomes even more striking when the controlling authority was taken into account; of the 713 events observed between 9 September 2012 and 26 May 2013, only six took place in districts that the United States Agency for International Development reported were under the control of forces loyal to the Assad regime. The remaining 707 incidents (99.3% of the total) occurred in areas that were either under rebel control (44%), Kurdish control (0.28%), whose authority was actively being contested (42%), or for which there was no data (12.6%). Furthermore, the destruction observed in solidly rebel districts frequently occurred far behind the front lines, in areas otherwise unaffected by signs of fighting. While multiple scenarios might result in such a pattern, the explanation that rebel districts have been subjected to ranged attack by aircraft, missile, and artillery fire is consistent with both media reporting and with the movements of military aircraft described above.

Figure 18: Cumulative incidence of damage and destruction over timeThe highly linear increase in observations suggests that the city has experienced a nearly constant rate of destruction (~3 incidents/day) for most of the study period.

Craters resulting from bursting artillery shells were observed most prominently in areas where the underlying terrain was conducive to their formation, such as soil, sand, or gravel. Less frequently, marks consistent with impact or near-surface airbursts also appeared on more durable surfaces, such as asphalt, concrete, or metal roofing materials. The sizes of craters ranged from the limits of the images' resolution up to ten meters in diameter (Figure 25[39]), and were often accompanied by debris and other signs of destruction (Figure 21[40]).

Aleppo is located at the crossroads of trade routes that date back to the 2nd millennium B.C. At the center of the city lies the Citadel of Aleppo, which contains evidence of continuous occupation dating back to the 10th century B.C. The citadel itself contains the remains of mosques, and palace and bath buildings and is an excellent example of Arab military construction between the 12th and 14th centuries A.D. The walled city around the citadel is laid out in a Greco-Roman style and contains 6th century Christian buildings, mosques and madrasas from the Ayybid and Mameluke era and more recent palaces and mosques from the Ottoman period. In 1986, the area around the citadel was inscribed onto the UNESCO World Heritage list as the Ancient City of Aleppo (Figure 22[41]).

Reports indicate that there has been heavy fighting within the Ancient City of Aleppo.8[42] In September 2012, damage to the Souq al-Madina, the world's largest covered market, prompted UNESCO Director-General Irina Bokova to comment that, "The human suffering caused by this situation is already extreme. That the fighting is now destroying cultural heritage that bears witness to the country's millenary history - valued and admired the world over - makes it even more tragic."9[43] On April 24, 2013, the destruction of Umayyad Mosque's 45 meter tall minaret again brought international attention to the threat to cultural artifacts in Aleppo.10[44]

In addition to these two high profile incidents, AAAS documented multiple instances of damage to structures within the Ancient City of Aleppo (locations noted in Figure 23[45]). In addition to visibly damaged structures, there were numerous examples of debris in streets, which could indicate damage to facades that could not be observed via satellite imagery.

Fighting in the northern section of the Ancient City has led to the destruction of at least ten multi-story structures (Figure 24[46]). Damage to this section began between 9 September 2012 and 12 October 2012, when burn marks appear on a roof (Figure 24A-B[46]). On 4 November 2012, debris appears in the road next to a possibly damaged multi-story building (Figure 24C[46]). By 15 December 2012, that building had collapsed (Figure 24D[46]) and the image from 1 March 2013 reveals another collapsed multi-story building (Figure 24E[46]). Between 1 March 2013 and 26 May 2013, three additional isolated structures were demolished (Figure 24F[46]). Additionally, a large block of at least four multi-story structures was destroyed.

Cultural artifacts outside the Ancient City have also been damaged. Figure 25 shows a large hole in the wall of a mosque just east of the UNESCO boundary appearing between 4 November and 15 December 2012. In the same image damage to a cemetery wall is visible and a ten meter wide crater has appeared in the middle of the cemetery.

Some of the most well-known historical sites in Aleppo have been damaged during the conflict (Figure 28[47]). Just west of the citadel lies the sprawling Souq al-Madina, the Umayyad Mosque (Great Mosque of Aleppo), and multiple smaller mosques and madrasas. Between 9 September and 12 October 2012, a 45 meter by 10 meter section of roof of the Souq al-Madina collapsed (Figure 28A-B[47]). Between 4 November and 15 December, an additional 20 meter by 9 meter section of roof also collapsed and fighting around the mosque had damaged the facade of a neighboring structure (Figure 28C-D[47]). A corner of the Halawiye Madrasa abutting the Umayyad mosque was also damaged between 24 February and 1 March 2013 (Figure 28E-F[47]). The worst damage, however, occurred between 1 March and 26 May 2013 (Figure 28G-H[47]). Over the course of fighting around the Umayyad Mosque, the 45 meter tall minaret in the northwest corner completely collapsed leaving a large hole in the wall of the mosque. In addition, a new section of the Souq al-Madina roof, measuring 90 meters by 30 meters, collapsed.

This analysis has shown widespread destruction within the Ancient City of Aleppo. At least ten multi-story buildings have been demolished over the course of the fighting. Major historical sites, such as the Umayyad Mosque and the Souq al-Madina, have also been extensively damaged. The battle has also damaged less famous mosques and disturbed gravesites in cemetaries. In addition to these instances of severe damage to buildings, multiple roadblocks and instances of debris in the street were noted within the UNESCO Ancient City boundaries. This implies that the damage documented here does not represent the full extent of fighting within this area.

IV. Conclusion

Space-based monitoring of the conflict in Aleppo has revealed a steady and continuous trend of degradation to the city's buildings and infrastructure, including residential, religious, commercial, and industrial facilities. Roadblocks and other makeshift fortifications have continued to proliferate, with over a thousand visible in the latest imagery. Other signs of military activity, such as shell craters, armored vehicle tracks, and evidence of aircraft deployments are likewise visible, and are consistent with reports of ongoing combat involving heavy weaponry in civilian areas. Damage resulting from fighting has resulted in severe losses to the city's cultural heritage, both in the city as a whole as well as the area designated as a UNESCO World Heritage site.

Although large areas of the city remain intact - particularly in areas controlled by regime forces - contested areas or those controlled by the opposition have been heavily damaged (Figure 29[48]) and some have had substantial portions of their area completely destroyed. In some cases, entire city blocks have been razed, and destruction patterns consistent with aerial bombardment have appeared in areas otherwise untouched by obvious signs of fighting. Though other interpretations may be possible, this striking dichotomy in damage, in conjunction with direct observations of military activity, is consistent with reports that government forces have been using aircraft, missiles, and long-range artillery to bombard rebel-held areas. 11[49], 12[50]